1. Field of the Invention
The present invention generally relates to a linear motion rolling contact guide unit assembly, and, in particular, to a linear motion guide unit assembly including a rail extending straight over a distance, a slider unit which slidably moves straight along the rail and a plurality of rolling members interposed between the rail and the slider unit to thereby provide a rolling contact between the rail and the slider unit.
2. Description of the Prior Art
A linear motion rolling contact guide unit assembly is well known in the art, and it generally includes a rail extending straight over a desired length, a slider unit mounted on said rail for relative motion therewith and a plurality of rolling members, such as balls or rollers, interposed between the rail and the slider unit to thereby provide a sliding relative motion between the rail and the slider unit. A typical prior art linear motion rolling contact guide unit assembly is, for example, described in the earlier Japanese Patent Application No. 61-297806, which has been assigned to the assignee of this application and is hereby incorporated by reference. A U.S. Patent Application was filed in the U.S.A. on July 21, 1988 Ser. No. 07/222,605 claiming the Convention priority of the above-mentioned Japanese Patent Application No. 61-297806 and the description of the corresponding U.S. Patent Application is also hereby incorporated by reference.
Such a shell-type linear motion rolling contact guide unit assembly as shown in the above-mentioned patent application includes a guide rail which is formed from a thin metal plate by bending to have a generally U-shaped cross section including a flat bottom wall and a pair of side walls extending upright from the opposite sides of the flat bottom wall. And, a pair of guide grooves is formed one in each of the pair of opposite inner surfaces of the side walls of the guide rail, and the guide grooves extend in parallel each other and with the longitudinal axis of the guide rail. The slider unit is received in a space defined by the U-shaped guide rail for relative motion to the guide rail. The slider unit is provided with a pair of endless circulation paths, each including a straight load path section located opposite to the corresponding guide groove, a return path section and a pair of curved connecting path sections connecting the corresponding ends of the load and return path sections. A plurality of rolling members, such as balls or rollers, are provided in each of the pair of endless circulation paths so that a rolling contact is provided between the slider unit and the guide rail on opposite sides of the slider unit. That is, the rolling members located in the load path section of the slider unit come to be partly received in the corresponding guide groove of the guide rail, so that the rolling members which are partly received in the corresponding load path section and the guide groove provide a rolling contact between the guide rail and the slider unit.
However, in manufacturing such a so-called shell-type linear motion rolling contact guide unit assembly, the load path section of the slider unit was finished by plastic deformation processing or barrel processing so that the resulting load path section tended to be poor in dimensional accuracy and surface roughness. As a result, such a shell-type linear motion rolling contact guide unit assembly found applications only in drawer guides of office cabinets or the like where high precision was not required, and it could not be applied to high-precision measuring devices and audio and information processing equipment where high precision was required.
The linear motion rolling contact guide unit assembly disclosed in the above-described earlier patent application includes a slider unit which is comprised of a pair of identically structured plate-shaped slider unit halves which are fixedly combined together in a face-to-face relation. Wit this structure, the height of the slider unit may be minimized, which, in turn, contributes to make the height of the guide rail or its side walls shorter, thereby making the overall height of the assembly compact in size. In this earlier linear motion rolling contact guide unit assembly, a top or bottom half of an endless circulation path is defined in the main surface of each of the top and bottom plates, which are combined together with their main surfaces in contact o thereby define a pair of endless circulation paths therebetween.
However, although the structure shown in this earlier patent application is compact in size and it provides a high-precision type linear motion rolling contact guide unit assembly, difficulty is encountered in its manufacture. That is, in the structure shown in the earlier patent application, a feed-in port is provided at one end of the endless circulation path to thereby allow to feed a plurality of rolling members into the endless circulation path, and after insertion of a plurality of rolling members, an end plate is fitted into a gap defined between the pair of top and bottom plates to thereby plug the feed-in port. However, a linear motion rolling contact guide unit assembly of this type is normally of the size equal to or smaller than a palm of a human being and the rolling members, typically balls, have a diameter in a range between about 2 and 3 mm. Accordingly, difficulty is encountered when feeding a required number of such small-sized rolling members into the endless circulation path of the assembled slider unit.